"Mystery" crystal radio. There's not much to it; a coil, capacitor, a 1N34A germanium diode (detector) and a pair of Hi-Z headphones. Apparently named because it's a mystery why it works so well. It actually works so well, it's a bit loud on the ears! The quality is quite good; you really have to hear it to appreciate it.

The detector.

Hi-Z phones - made by Tower Manufacturing Co. of Boston Mass.

The schematic.

This the latest change

This is the honey comb coil I built.

I measured it to be 127 uH.

Basket weave coil.